Hydraulic apparatus with interconnected hydraulic units

ABSTRACT

Two hydraulic units, each operable as a pump or motor, are mechanically connected by a coupling transmission which can be engaged and disengaged. Valves are hydraulically connected to the units, so that a single unit can be operated as a pump or motor, that both units can be simultaneously operated as pumps or motors, and so that the two units form a hydrostatic transmission.

limited States Patent [151 3,643,433

l vielmaier 1 lFelb, 22, 119 72 [54] ll-llYlll lPtAlllLllfi APPARATU Wil'llllll Inventor: Dieter Widniaier, Fellbach, Germany Assignee: Robert Bosch Gmhfill, Stuttgart, Germany Filed: May 7, 1970 Appl. No.: 35,427

Foreign Application llriority Data June 10, 1969 Germany ..P 19 24 010.9

US. (31. Mi/53 A, 91/473, 417/236,

417/237, 417/426 lint. 1C1 ..1F'16d 31/02 Wield oil Search ..60/53 A, 53 B, 52 US; 91/473;

[56] lteterenees Cited FORElGN PATENTS OR APPLICATIONS 818,141 10/1951 Germany ..60/53 A Primary ExaminerEdgar W. Geoghegan Attorney-Michael S. Striker ABSTRACT Two hydraulic units, each operable as a pump or motor, are mechanically connected by a coupling transmission which can be engaged and disengaged. Valves are hydraulically connected to the units, so that a single unit can be operated as a pump or motor, that both units can be simultaneously operated as pumps or motors, and so that the two units form a hydrostatic transmission.

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PAIENTEDFEB22 m2 3. 643 A33 SHEET 8 OF 6 INVENTOR. Diefer W/DMA g/Q HYDRAULIC APPARATUS WITH INTERCONNECTIED HYDRAULIC UNITS BACKGROUND OF THE INVENTION The present invention relates to a hydrostatic transmission with at least two hydraulic units arranged in a common hous ing side by side, and preferably comprising axial piston pump units of which at least one is connected with a drive shaft, while a transmission is provided for connecting the rotary parts of the two hydraulic units.

A hydraulic apparatus of this type is disclosed in the Swiss Pat. No. 463,962 in which all units are permanently connected and continuously rotate when only one unit is driven, or drives. The apparatus is used as a multiple pump or multiple motor, and has the disadvantage that, in the event that only small output is required, nevertheless both units have to operate so that the mechanical losses are greater than as if only one pump would be used. Furthermore, the apparatus can only be used as a pump, or as a motor.

SUMMARY OF THE INVENTION It is one object of the invention to overcome the disadvantages of known hydraulic apparatus including at least two hydraulic units, and to provide an apparatus which, under particular operational conditions, has very low losses, and which can be adapted to different load requirements.

With these objects in view, the invention provides between two hydraulic units, a mechanical transmission which can be selectively engaged when operation of both units is required, or disengaged when only one unit is to operate, or if one unit is to be operated as a pump and the other as a motor to form a hydrostatic transmission.

The apparatus of the invention has the advantage that, if only a small output is required, only one hydraulic unit is operated, while the other is stopped, resulting in a reduction of mechanical and hydraulic losses, leakage, and general wear of the parts.

An embodiment ofthe invention comprises at least first and second hydraulic units having first and second stator means and first and second rotary means, respectively; connecting means having an engaged condition mechanically connecting the first and second rotary means for rotation so that the first and second hydraulic units simultaneously operate as pumps when the first rotary means is driven, and as hydraulic motors when a fluid medium under pressure is supplied to the first hydraulic unit, and a second disengaged condition disconnecting the first and second rotary parts so that only the first unit operates as a pump or motor, respectively; and operating means for placing the connecting means selectively in the engaged and disengaged conditions. The apparatus comprises a casing means enveloping both hydraulic units.

In one embodiment of the invention, the connecting means include two meshing gears respectively connected to the rotary means of the first and second units for rotation, and one of the gears is shiftable in axial direction to disengage the respective other gear so that the two units are separated. In another embodiment, two gears fixed on the first and second rotary means of the first and second units, do not mesh directly, but are connected by a third gear which can be shifted to an inoperative position.

The first hydraulic unit has rotary means including a shaft which can be used as a drive shaft when the unit is driven with or without the second unit, depending on the condition of the connecting means. The shaft ofthe rotary means of the second unit is advantageously coupled with an output shaft if the first unit is driven as a pump and the second unit is driven by the same as a hydraulic motor of a hydrostatic transmission. The apparatus of the invention is advantageously used in a car in which it can be used for driving the wheels, but when the destination is reached, the apparatus operates as a single or multiple pump driving hydraulic motors of loading apparatus, such as fork lifts, or operates dredges provided with hydraulic motors.

In the event that three hydraulic units are provided, more combina ons are possible, namely operation as a single pump, double pump and triple pump or as single motor, double motor or triple motor, or as a hydrostatic transmission with a separate auxiliary pump. The apparatus has the advantage ofa very compact construction, so that it can be transported and used at any destination either as hydrostatic transmission, or as pump or as hydraulic motor.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is an axial sectional view illustrating an apparatus of the invention having two hydraulic units;

FIG. 2 is a fragmentary sectional view illustrating a modiii cation of the embodiment of FIG. I;

FIG. is a plan view of the apparatus shown in FIG. I or FIG. 2,;

FIG. 4 is a fragmentary elevation, partially in section, illustrating a detail of the embodiment of FIG. ll;

FIG. 5 is a fragmentary plan view illustrating a detail of FIG.

FIG. 6 is a schematic and partially diagrammatic view illustrating two hydraulic units having control valve means in a first operational condition;

FIG. '7 is a schematic view corresponding to FIG. 6 and illustrating the apparatus in another operational condition;

FIG. 8 is a schematic and partially diagrammatic view illustrating a modification of the embodiment of FIGS. 6 and 7 in another operational condition;

FIG. 9 is a plan view illustrating modified connecting means for the two units;

FIG. 10 is a diagrammatic view illustrating various combinations of an apparatus according to the invention comprising three hydraulic units; and

FIG Ill is a schematic view illustrating a modification of the connecting means of the two units.

DESCRIPTION OF THE PREFERRED EMBODlMENTS Referring first to FIG. I a housing or casing has a first portion I, and a second cover portion I and envelops two hydraulic units 2 and 3. The hydraulic unit 2 has a cylinder body t which is rotated by a drive shaft 5 which is supported in roller bearings 7 and El, and driven from a prime mover, not shown, which includes an output member connected with the gear 6. Cylinder bores II) are provided in the cylinder body for receiving reciprocable pistons 9 abutting a swashplate 12 which is nonrotatable, but tiltable about a pivot Ill whose axis intersects with the axis of drive shaft 5. Cylinder body 4} is biased by a spring llEI abutting a flange on drive shaft 5 and a ring secured to cylinder body I, so that the end face of cylinder body I slidingly abuts a smooth surface of a stationa ry member M mounted in the casing cover portion 1. Member M has bores 2b and 29 communicating with the cylinder bores 10 during rotation of cylinder member 4. This type of axial piston pump is well known, and not an object of the invention.

Cylinder body 4 is surrounded by a ring gear 15 which may be a portion of the cylinder body, or a separate ring shrunk onto cylinder body I, or otherwise fixed on the same.

Spaced from drive shaft 5, and parallel to the same, a stationary tubular shaft I6 is mounted in the casing on which another cylinder body I9 is mounted for rotation by means of roller bearings 17 and lb. Cylinder body 19 has axial cylinder bores 21) in which pistons 21 are reciprocable which slidably abut a swashplate 235 which is nonrotatable, and mounted on a pivot 22 for tilting movement about an axis intersecting with the axis ofshaft l6.

The cylinder body 19 is urged by spring 24, which is located in the space between the tubular shaft 16 and the cylinder body, against a smooth surface of a member 25. Spring 24 abuts two rings, one of which is secured to shaft 16, and the other of which is mounted on the cylinder body 19. On the outer periphery of the rotary cylinder body 19, a gear ring 26 is mounted for rotation with cylinder body 19, but axially movable on the same between a position abutting a nose 27 of cylinder body 19, and being disengaged from gear and another position meshing with gear 15 which is secured to cylinder body 4, so that the two rotary cylinder bodies 4 and 19 are connected for rotation. Stationary members 14 and 25, serving as valve plates are nonrotatably mounted in recesses of the casing portion 1", but it is advantageous to leave a little play for member 25 so that it can abut the end face of the rotary cylinder body 19 when the same assumes different angular positions.

Stationary or control members 14 and 25 have part-circular grooves 28, 29 30, respectively, of different circumferential length, as best seen in FIG. 3. The grooves 28 and 31 are connected by a conduit 32 shown in dash and dot lines in FIG. 1, and partly sectioned as shown in FIG. 3. Conduit 32 has a widened conduit portion 33 in which a check valve 34 is mounted in such a manner that it either abuts a seat 34 formed in housing portion 1" registering with the portion of conduit 32, or an annular shoulder 34". Conduit 32 is connected by branch conduit 32 with a main conduit 35. In the position of check valve 34 shown in FIG. 3, conduit 32 and conduit 35 are disconnected from groove 31 and connected with groove 28 in control member 14, while in the other position of check valve 34, abutting shoulder 34", conduit 35 communicates also with groove 31 in control member 35.

The grooves 29 and 30 are connected by a conduit 36, shown in broken lines in FIGS. 1 and 3, and open into a main conduit 37.

The two swashplates 12 and 23 are connected to each other for tilting movement by a linkage shown in FIG. 1, and can be simultaneously turned about pivots 11 and 22, respectively, by shifting rod 40 connected to the piston of a servomotor 38 which is operated by a control rod 39, so that adjustment of control rod 39 causes simultaneous displacement of shifting rod 40, at a greater power for tilting the swashplates 12 and 23 by which the output of the hydraulic units 2 and 3 is adjusted.

It is also possible to provide each of the swashplates 12 and 23 with an independent servomotor and control rod so that the two units are differently adjusted if required, or to fix one ofthe swashplates l2 and 23, and to adjust only the respective other swashplates. As is apparent from FIG. 3, the main conduits 35 and 37 communicate with both hydraulic units 2 and 3. It is also possible to provide separate main conduits for each hydraulic unit, in which event the check valve 34 can be omitted.

As shown in FIGS. 4 and 5, the gear ring 26 on cylinder body 19 can be shifted in axial direction by a shifting fork 42 which has part-circular arms ending in U-shaped members 43, whose legs engage the gear ring 26 at opposite ends. Shifting fork 42 is operated by a bar 44 which projects out of the housing. Members 44,42, 43, are operating means for placing the connecting means 26, 15 either in an engaged condition in which the rotary means 4, 9 and 19, 21 are connected for rotation and a disengaged condition in which ring gear 26 is axially displaced and does not mesh with gear 15 so that the two rotary means 4, 9 and 19, 21 are in a disengaged condition. Ring gear 26 is guided by keys 45 in groves of cylinder body 19 for axial movement, connected with cylinder body 19 for rotation.

Instead of the positive connection by keys 45 and axial grooves, a friction connection can be provided and, for example, operated by electromagnetic means. This has the advantage that the gear ring 26 need not be axially shiftable on the cylinder block 19, but freely rotates with gear 15 if the electromagnetic means is not energized, but is magnetically connected with cylinder body 19, when the electromagnetic means, not shown, is energized.

Assuming that the mechanical transmission 15, 26 is in the engaged condition, cylinder body 19 is rotated when drive shaft 5 rotates cylinder body 4. Since gears 15 and 26 have the same number of teeth, the two cylinder bodies rotate at the same speed. In the engaged condition of the connecting means 25, 26 both hydraulic units 2 and 3 operate as pumps. Low pressure and suction prevails at the grooves 29 and 30, and the pressure medium is sucked through the main conduit 37 into conduit 36 from a reservoir or container, not shown in FIG. 1 and 3. During rotation of the cylinder bodies 4, 19, pistons 9 and 21 also rotate and are axially shifted by the swashplates l2 and 23 so that the pressure medium is pumped into the,

grooves 28 and 31 and flows through conduit 32 from hydraulic unit 3 through the open check valve 34. Main conduit 35 is connected to one or several consumers, such as hydraulic motors. If the required volume of pressure medium is low, so that the two hydraulic units are not fully utilized, gear ring 26 of the hydraulic unit 3 is shifted to be disengaged from gear ring 15, so that no torque is transmitted from the rotary means 4, 5 to the cylinder body 19 and hydraulic unit 3 is rendered inoperative so that only hydraulic unit 2 pumps the pressure medium.

The check valve 34 prevents flow of pressure medium through conduit 32 to the groove 31 and the cylinder bores 20, which would cause rotation of cylinder body 19 if swashplate 23 is in a slanted position. When only the first unit 2 operates as a pump, check valve 34 abuts the seat 34' and prevents communication between the hydraulic units 2 and 3.

However, the check valve 34 can be omitted if the swash plate 23 is placed in a neutral position when hydraulic unit is to operate as a single pump. In such an arrangement the linkage between swashplates l2 and 23 must be omitted, and the swashplates independently operated.

Due to the fact that only hydraulic unit 2 operates if the load is sufficiently small, friction losses, leakage losses, and other hydraulic losses are reduced so that the efficiency ofthe apparatus is increased, as compared with prior art. Furthermore, hydraulic unit 3 is not subjected to wear when disengaged from the rotating unit 2.

When the apparatus is to operate in a condition in which both hydraulic units 2 and 3 operate as hydraulic motors, the gear 26 is shifted to a position meshing with gear 15. A medium is pressed at high pressure into the main conduit 35 from where it flows through conduit 32 into grooves 28 and 31 of control members 14 and 25. The pressure in the cylinder bores urges the pistons 9 and 21 against the swashplates l2 and 23 so that a reaction torque is produced by which both cylinder blocks 4 and 19 are rotated. While the tor ue of cylinder block 4 is directly transmitted to shaft 5, the torque of cylinder block 19 is transmitted through the connecting gears 26 and 15 to cylinder block 4 and by the same to shaft 5, which serves now as the single output shaft for both units.

If a lesser output torque is required at shaft 5, the hydraulic unit 3 is rendered inoperative by placing ring gear 26 in the disengaged position. When both units are operated as hydraulic motors, it is necessary to open check valve 34 which can be carried out in a well-known manner by mechanical or hydraulic devices.

FIG. 2 illustrates a modification in which each unit is an axial piston pump in which the wobble plates 49 and 50 rotate, while cylinder bodies 47, 48 are stationary. The drive shaft 51 is mounted in the casing and in the stationary cylinder body 47 for rotation, and wobble plate 49 is fixedly secured to the same. Wobble plates 50 is also mounted in the casing and in the cylinder body 48.

Wobble plate 49 has a gear ring 52 integral therewith, and wobble plate 50 has a gear ring 53 which is connected therewith for rotation, but is shiftable in axial direction between two stops 54 and 55 between a position meshing with gear ring 52, and a position spaced from the same. A shifting means, similar to the shifting means 44, 43, 42 described with reference to FIGS. 4 and 5, is provided, for axially shifting ring gear 53, as schematically indicated in FIG. 2 by an arrow.

A modification of the connecting means is illustrated in FIG. 9 which shows a pair of gear rings corresponding to gear rings and 26 in the embodiment of FIG. l, and to gear rings 52 and 53 in the embodiment of FIG. 2 are fixedly secured to the respective cylinder blocks or wobble plates for rotation therewith in a position in which they do not mesh. A third connecting gear 54 is mounted on a shaft 56 for axial shifting movement between a position spaced from the gear rings of the two units 2 and 3, and a position meshing with both gear rings so that the respective rotary means of the two units 2 and 3 are connected for rotation. Instead of axially shifting gear 54 and shaft 54' gear 54 can be fixed on a lever arm and pivoted between the engaged condition meshing with the two gear rings and the disengaged position spaced from the same.

The apparatus shown in FIGS. 6 and 7 permits the use of two hydraulic units 2 and 55 not only as single or double pumps, or hydraulic motors, but also as a hydrostatic transmission. The hydraulic unit 2 has a rotary means which includes the first shaft 5, and in contrast to the embodiment of FIG. I, the hydraulic unit 55 has a rotary means secured to a second shaft 56 which replaces the stationary shaft 16 of the embodiment of FIG. l. The cylinder block of hydraulic unit 55 carries a gear 26 meshing with gear 15 of the hydraulic unit 2 in the position of FIG. 6, and being axially displaced from the same in the position of FIG. 7. This shifting of gear ring 26 in axial direction is accomplished by a shifting means including a forked member 43 which embraces gear 26.

An output shaft 59 is axially aligned with the second shaft 56 and can be coupled with the same by means ofa coupling sleeve 60 carried by the shifting means 6ll which may be manually operated to simultaneously shift a forked member 43 with gear 26, and the coupling sleeve 66 to a position surrounding the ends of shafts 56 and 59, which are fluted or otherwise provided with axial grooves cooperating with axially extending projections on the inner surface of coupling sleeve 60. In the position of FIG. 6, the two cylinder blocks of the two rotary units 2 and 55 are connected for rotation and shaft 56 is separated from the output shaft 59, whereas in the posi tion of FIG. 7, the rotary units are separated since gear 26 is axially displaced, while shaft 56 is connected for rotation with output shaft 59.

It is evident that separate shifting means could be provided for gear 26 and for coupling sleeve 60. Instead of the coupling sleeve 60 an electromagnetic coupling could be provided for coupling shafts 56 and 59.

FIGS. 6 and 7 illustrate conduits and valves controlling the operations of the apparatus in a schematic diagrammatic manner. A conduit 62 corresponding to conduit 32 is FIGS. l and 3, is connected with a first valve 63 which has three positions I, II, and III. Valve means 63 has three ports a, b, c for differently connecting conduit 62 with a conduit 66 connected with a consumer, such as a hydraulic motor, not shown, and with a second portion of conduit 62 which communicates with the hydraulic unit 55 as described for conduit 32 in the em bodiment of FIGS. l and 3. Conduit 65 corresponds to conduit 36 of the embodiment of FIGS. 1 and 3, connecting the hydraulic units 2 and 55, and being connected with a conduit 66 in which a second valve having two positions land II is provided. Conduit 66 has an end portion located in a container 68 for fluid medium. Another conduit 69 also communicates with conduit 65, and can be connected by valve 6'7 in the position of FIG. 7 with an auxiliary pump 76 which pumps fluid medium from the container 65. A conduit "ll, ending in container 68, is connected with a port of valve 67 which connects con duit 71 with auxiliary pump 70 in the position II shown in FIG. 6.

The apparatus functions as a double pump in the condition shown in FIG. 6. The gear rings of the two hydraulic units 2 and 55 mesh, coupling sleeve 66 is in a position separating shaft 56 from output shaft 59, valve 63 is in the position II, and valve 67 is in the position ll thereof. When shaft 5 is driven by a prime mover which applies a torque to the same, a pressure medium is sucked out of container 68 through conduit 66 and a duct in valve 67, and flows into the low pressure conduit 65 and from there to the suction chambers of the two hydraulic units 2 and 5.5 operating as pumps, and discharging the medium through conduit 62 and ducts in valve 63 which connect both portions of high-pressure conduit 62 with the port C to which the consumer conduit 64 is connected.

The medium pumped by the auxiliary pump 76 flows through ducts in valve 67 into the return conduit 7ll from where it is discharged into the container so that auxiliary pump 76 idly circulates the medium.

When the apparatus operates as a double hydraulic motor, high-pressure medium is supplied through the conduit 64 and flows into the two portions of conduit 62, and out of conduit 65, 66, a duct in valve 67 into container 65. The rotary cylinder blocks of units 2 and 55 are driven, and rotate shafts 55 and 56. However, only shaft 5 is used as output shaft in the position ofcoupling sleeve 66 in FIG. 6.

If it is desired that only one unit of the apparatus should operate as pump or motor, respectively, the shifting means 6i is operated to the FIG. 7 position and the gears 26 and I5 disengage. Valve 63 is shifted to the position III, while valve 67 remains in position II. The shaft 5 is driven to operate unit 2 as a pump, and the pressure medium flows from unit 2 through conduit 62 to port 6 which is now connected with the consumer conduit 66. No pressure medium can flow from unit 2 into unit 55 so that the same is not operated. In this arrangement, it is not necessary to provide a checlt valve in conduit 62, as in the embodiment shown in FIGS. l to t.

When shifting means 62 is operated so that gear 26 is separated from gear 115, and when shaft 56 is connected with output shaft 59 by the coupling sleeve 60, as shown in FIG. 7, the apparatus functions as a hydrostatic transmission if valve 63 is placed in the position I, and valve 6'7 is placed in the position I thereof. Drive shaft 5 is driven by prime mover, not shown, and the hydrostatic transmission operates in a closed circulation since the high-pressure medium pumped by the hydraulic unit 2 is supplied to the hydraulic unit 55 through conduit 62 and valve 63 due to the fact that in the position I of valve 63, a duct connects the ports a and b which communicate with conduit 62. The pressure medium looses its pressure in the unit 55 which is operated as a hydraulic motor driving shaft 56 and through coupling sleeve 66 also output shaft 59. Since the apparatus functions with a closed circulation it is necessary to compensate leakage losses. For this purpose the auxiliary pump pumps, in the position I of valve 67, medium from container 65 through conduit 69 to the inlet conduit 65 of the two hydraulic units. By this additional amount of fluid medium, the leakage losses are compensated.

The torque supplied by the primer mover to a drive shaft 5 of the hydraulic unit 2 is transformed into pressure of the pumped fluid medium and supplied to the unit 55 which operates as a motor so that output shaft 59 is driven, and the apparatus functions as a hydrostatic transmission which may be used in a motorcar for driving the wheels. The connection between container 65 and conduit 66 is interrupted by valve 67 in its position I.

All shiftable parts, such as gear 26, coupling sleeve 66 and valves 63 and 67 can be electromagnetically, mechanically or hydraulically operated. It is only necessary to operate the shiftable means so that the valves 63 and 67 and gear 26 are placed in the positions explained above. Electrical or hydraulical remote control devices can be used for these shifting operations.

When the apparatus operates as a single pump 2, with valve 63 in position III, and valve 67 in the position II, as shown in FIG ti, it is only necessary to move gear rings 26 to the engaging position meshing with gear 15, and the apparatus operates as hydrostatic transmission.

Valve 63 is advantageously constructed as a slide valve built into the cover part ll ofthe casing. The bore in the valve housing in which the valve slide 63 moves, is preferably parallel to drive shaft Conduits 62 and 66 open into the valve housing at ports a and c.

Valve 72 and valve 67 used in the embodiment of FIG. 8, permit a reversing of the hydrostatic transmission so that the output shaft 59 rotates opposite to the direction in which it rotates in the apparatus shown in FIGS. 6 and 7. The swashplates 12 and 23 are not connected by a linkage in the apparatus of FIG. 8, and swashplate 12 is tilted from the position shown in FIG. 6 to the position shown in FIG. 8, passing through a neutral position. Valve 72 has five ports a to e in the valve housing, and is shiftable between three positions I, II, and Ill. Port a is connected to conduit 64, conduit 73, has two portions connected by a duct between the ports b and c, and a conduit 74 has two portions connected by a duct between ports d and e in the position III of valve 72.

Conduit 66' is directly connected with conduit 74, and conduit 69' is connected by check valve 76 with conduit 74. Conduit 69 is connected by a check valve 75 with conduit 72 which corresponds to conduit 73. Check valves 75 and 76 open toward conduits 72 and 74.

When valves 67 and 72 are in the position I, the apparatus operates as single pump and motor, but the swashplate 12 is tilted in the opposite direction from that shown in FIG. 6. The pressure medium flows from conduit 73 from port b to port a and into the consumer conduit 64. No pressure medium can flow from hydraulic unit 2 to hydraulic unit 55, and pressure medium is sucked into hydraulic unit 2 from container 68 through conduit 66.

When valve 72 is placed in the position II, and valve 67 is placed in the position I, the apparatus operates as double pump or double motor. The high pressure conduits 73 and 7311 open into ports b and c, and are connected by ducts of valve 72 with port a and conduit 64 which receives pressure medium when both units operate as pumps and supply pressure medium when both units operate as motor.

In the position III of valve 72 and position II of valve 67, the apparatus operates as a hydrostatic transmission. Gears 26 and are disengaged, as shown in FIG. 8, and clutch 60 is engaged and connects shaft 56 with the output shaft 59. If swashplate 12 is tilted to the opposite position, that is to the position of FIG. 6 instead of the position of FIG. 8, hydraulic unit 2 operates as pump and pressure medium is pressed into conduit 73, flows into conduit 73a, and drives hydraulic unit 55 as a hydraulic motor. Conduit 74 is the low pressure conduit into which auxiliary pump 70 pumps the pressure medium from container 68 at low pressure through conduit 69 and check valve 76. Check valve 75' is closed.

Hydraulic unit 55, and more particularly its rotary means including shaft 56, rotate in the opposite direction of rotation when swashplate I2 is tilted through the neutral position to the tilted position shown in FIG. 8. Conduit 74 is now the high-pressure conduit, and conduit 73 is the low-pressure conduit, and receives pressure medium from the auxiliary pump 70 through conduit 69', connecting conduit 75, and check valve 75. No pressure medium can flow out of conduit 74 into conduit 69' since the check valve 76 closes.

While the invention has been described with reference to two hydraulic units, it will be understood that three or more units can be used by applying the principle of the invention. The schematic and diagrammatic view of FIG. 10 illustrates possible operational conditions of three hydraulic units 77, 78, and 79. Only hydraulic units 77 and 78 have shafts 77 and 78' which can be used as drive shafts. Unit 79 may be constructed as unit 3 in FIG. 1, with a stationary tubular shaft 69. The small circles connecting large circles schematically indicate that the respective two hydraulic units are not connected to each other, and crosses between two large circles indicate that the respective two hydraulic means are connected by mechanical connecting means as described above.

In the operational condition A, the rotary means of hydraulic units 77 and 78 are not mechanically connected for rotation, but unit 77 and unit 78 are hydraulically connected to form a hydrostatic transmission. The hydraulic unit 79 is mechanically connected with unit 77 for rotation, and is thus driven to operate as a pump. The operational condition A is suitable for a vehicle with a hydrostatic drive, with an auxiliary hydraulic motor to which pressure medium is supplied by the unit 79.

In the operational position B, the units 77 and 78 are not mechanically connected for rotation, and the rotary means of unit 77 and unit 79 are connected by an engaged connecting means to each other. When unit 77 is driven by prime mover as a pump, unit 79 is also operated as a pump, while unit 78 is not driven and inoperative.

In the operational condition C, unit 77 is mechanically connected with units 78 and 79 for rotating the rotary means of the same. Unit 77 may be driven by a prime mover so that all three units operate as pumps, or if the pressure medium is su pplied to the units, all three units operate as motors.

In the operational condition D, the rotary means of units 77, 78 and 79 are mechanically disconnected. Only unit 77 operates as a pump.

A common housing or casing is provided for all three units and the mechanical connection is advantageously obtained by gear rings corresponding to gear rings 15 and 26 described with reference to the two unit apparatus shown in FIG. 1. l

In the embodiments of FIG. 1 and 3, gear rings 15, 26 aiid 52, 53 are fixed to the rotary cylinder bodies, and to the rotary swashplates, respectively, within the casing. In the modified embodiment shown in FIG. 11, gears 80 and 81 are respectively mounted on the shafts of the rotary means of the units 2 and 3. Gear 80 is fixed to shaft 5, while gear 81 is connected with the shaft 56 of unit 3 for rotation, but is axially shiftable on the same by means ofa fluted portion 82 of shaft 56. As indicated by a double arrow, gear 81 can be shifted in axial direction to a position in which it does not mesh with gear 80, so that the rotary means of the two units 2 and 3 can independently operate as a hydrostatic transmission, or so that the unit 3 can be rendered inoperative and only unit 2 is operative.

However, since in hydraulic units of the type described above, transverse hydraulic forces occur, it is advantageous to place the mechanical connecting means in the embodiment of FIGS. 1, 6 and 7 in the line in which the resultant of these transverse forces is located. In certain conditions, it is advantageous to place the gears 15, 26 at the upper ends or lower end of the cylinder bodies 4 and 19, instead in the middle as shown in FIGS. 1, 6 and 7.

It is evident that the rotary means of the cooperating hydraulic units can be connected by mechanical coupling connecting means different from the gears described above. For example, V-belt drives or chain drives may be used, which, however, are impractical in the embodiments of FIGS. 1 and2 since it is not possible to axially shift chain wheels or belt pulleys. The embodiment of FIG. 11 is more suitable if the two connecting elements are provided with a synchronizing device of the type known from synchronized gear transmissions used in motorcars. Also one of the pulleys or gears can be connected with the respective shaft by an electromagnetic coupling means. Irrespective of whether gears, chain wheels or pulleys are used, the connection can be disengaged without requiring axial shifting which has the additional advantage that coupling and disengaging, respectively, of the rotar means of the two units is possible during rotation.

Since synchronizing apparatus requires considerable space, it is difficult to use it in the embodiments of FIGS. 1 and 2 in which the space in the casing is limited. The embodiment of FIG. 11 .is suitable for such a construction, since there is sufficient space below the hydraulic units 2 and 3, and the diameters of the shafts of the units are small compared with the diameters of the cylinder bodies. Since synchronizing devices for mechanical transmissions are well known, they have not been illustrated.

The apparatus of the invention can be used for numerous purposes. For example, for the hydraulic drive of apparatus whose fluid requirements vary considerably, for example, winches, cranes, and hydraulic apparatus which may be driven by a single unit or by two units of the invention operating as pumps. Furthermore, motorcars with hydraulic drives which have to lift loads-at the place'of destination, or have to drive apparatus. For example, a large crane may be transported to a building site with the apparatus serving as hydraulic drive, and then be operated by a double unit pump to lift heavy loads so that additional hydraulic apparatus for operating the crane can be eliminated. Axial piston hydraulic units have been described and illustrated, but it will beunderstood that radial piston hydraulicunits can also be used. During operation of the apparatusas a hydrostatic transmission, it is not necessary to provide the coupling means 60 for coupling shaft 56 with output shaft 59, and shaft 56 can be extended out of the housing and serve as anoutput and'drive shaft for a machine.

It-will be understood that each of the elements described above, or two or more together, may also find a useful applicationin other types of apparatus comprising interconnected hydraulic units, differing from the types described above.

While the invention has been illustrated and described as embodied in a plurality of mechanically and hydraulically interconnectedhydraulic units operable by valves and coupling means between different operational conditions to serve as pumps, hydraulic motors, or hydraulic-transmissions, it is not intendedi to b'eflimitedto thedetails shown, since various modificationaandstructural changesmay be madewithout departing. in any way from-the spirit of the present invention.

.1 Without.further 'analysis, the foregoing will so fully reveal the gist of thepresent in vention:that otherscan by applying current: knowledge readily adaptit forvarious applications witho'dtcrnitting features that, from the standpoint .of prior art; fairly. constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the mcaningand range of equivalence ofthe following claims.

What is claimed as new and desired to be protectedby Letters Patent is set forth in the appended claims.

1'. Hydraulicapparatus with interconnectedhydraulic units, comprising, in combination, at least first and second hydraulic units having-first and second stator means and first and second rotarymeans, respectively; connecting means having an engaged position mechanically connecting said first and second rotary means for rotation sothat said first and second hydraulic units simultaneously operate as pumps when said first rotary means is dr iven, and as hydraulic motors when. a fluid medium underpressure is supplied to said first hydraulic unit, and a, disengaged condition disconnecting said first and second rotary means .so that only said-first unit operates as pump .ormotor, respectively; and operating means for placing said connecting meansselectively in said engagedand disengaged conditions. h

12. Hydraulic apparatus as claimed'in claim 1 comprising casing means enveloping said hydraulic units;

3'. Hydraulic apparatus as claimed in claim 2 wherein said casing means include first and second high-pressure ports and first and second low-pressure :ports for said first and second hydraulic units, respectively; high-pressure conduit means and low-pressure conduit means communicating with said first and second highpressure ports, and with said first and second lowpressure ports, respectively; and check valve means separating said second high-pressure port from said first high-pressure port and said high-pressure conduit means. w 4. Hydraulicapparatus as claimed in claim 1 wherein said first rotary means includes a shaft; and wherein said second hydraulic unit includes a stationary shaft secured to said second stator means and supporting said second rotary means for rotation.

5. Hydraulic apparatus as claimed in claim 1 wherein said connecting means include a first gear fixedly secured to one of said first and second rotary means for rotation therewith, and a second gear mounted on the other of said first and second rotary gearsfor rotation therewith about parallel axes in an engaged position meshing with said first gear, and for axial movement to a disengaged position; and wherein said operatin'gmeanslis connected with said second gear for moving the same between said engaged and disengaged positions.

6. Hydraulic apparatus as claimed in claim 1 wherein said connecting means include first and second gears fixedly secured to said first and second rotary means for rotation therewith about parallel axes, and athird gear operable by said operating means between a position meshing with said first and second gears for connecting the same for rotation in said engaged condition ofsaid connecting means, and a disengaged position spaced from at least one of said first and second gears.

7. Hydraulic apparatus as claimed in claim 1 wherein said first and second rotary means include first and second slanted wobble plates connected by said connecting means in said engaged position for rotation; and wherein said first and second stator means include first and second cylinder blocks, and first and second pistons in the same, respectively.

8. Hydraulic apparatus as claimed in claim 1 wherein said first and second stator means are first and second slanted swashplates; and wherein said first and second rotary means include first and second cylinder blocks and pistons in said cylinder blocks sliding on said swashplates; and wherein said connecting means connect in said engaged. condition said cylinder blocks for rotation. v l v 1 I x 9. Hydrauliclapparatus as claimedgin claim, fdwhereinsaid first andsecond cylinder blocks have parallel axes of rotation; wherein said first and second swashplatesare mounted fortilt ing. movementabouttwo parallel axes respect ivelyintersecb ing with said axes of rotatiomand comprising a control means common to both said hydraulic units andoperable for simultaneously tilting said first and second swashplates'for simultaneously adjusting the output of said first and second hydraulic units.

10. Hydraulic apparatus as claimed in claim 1 wherein said first rotary means includesa first shaft adapted to be driven by a prime mover when said first hydraulic unit operates as a pump; wherein said second rotary means includes a second shaft adapted to serve as an output shaft when said second hydraulic-unit is operated as a hydraulic motor; and comprising valve means having acontrol position for hydraulically connecting said first and second hydraulic units-when said connecting means is in said disengaged condition so that said first hydraulic unit operating as a pump drives said second hydraulic unit operating as a hydraulic motor whereby said first and second hydraulic units form a hydrostaticftransmiss1on.

. 11; Hydraulic apparatus as claimed in claim 10 comprising an output shaft; and coupling means having a disengaged position and a coupling position for connecting said second shaft with said output shaft when said firstshaft is driven by a prime mover and said first and second hydraulic units operate as a hydrostatic transmission.

12. Hydraulic apparatus as claimed in claim 11 wherein said operating means include shifting means connected with said coupling means and operating the same simultaneously with said connecting means so that said connecting means is in said disengaged condition when said coupling means is in said coupling position.

13. Hydraulic unit as claimed in claim 12 wherein said con necting means includes a gear transmission connecting said first and second rotary means for rotation in said engaged condition, and including a gear movable to an inoperative position for disconnecting said first and second rotary means in said disengaged condition; wherein said second shaft is axially aligned with said output shaft; and wherein said coupling means includes a coupling sleeve mounted on said second shaft, and for axial movement into engagement with said output shaft; and, wherein said shifting means is connected with said gear and said coupling sleeve for simultaneously displacing the same.

14. Hydraulic apparatus as claimed in claim 10 comprising an auxiliary pump; and wherein said valve means in said control position hydraulically connects the output of said auxiliary pump with the input of said first hydraulic unit operating as a pump, said valve means having another position disconnecting said auxiliary pump from said first hydraulic unit.

15. Hydraulic apparatus as claimed in claim 1 wherein said first rotary means includes a first shaft adapted to be driven by a prime mover so that said first rotary unit operates as a pump; wherein said second rotary means includes a second shaft adapted to serve as an output shaft when said second hydraulic unit operates as a hydraulic motor; comprising valve means and conduit means hydraulically connecting said first and second hydraulic units, said valve means being operable between a first control position in which in said disengaged condition of said connecting means said first hydraulic unit operates as a pump, a second control position in which in said engaged condition said first and second hydraulic units both operate as pumps, and a third control position hydraulically connecting said first and second units so that in said disengaged condition of said connecting means, said second hydraulic unit operates as a hydraulic motor hydraulically driven by said first unit operating as a pump and forming a hydrostatic transmission with the same.

16. Hydraulic apparatus as claimed in claim comprising an auxiliary pump and a container for a fluid medium communicating with the low-pressure inlet of said auxiliary pump; and wherein in said third control position said valve means hydraulically connect the high-pressure outlet of said auxiliary pump with the'input of said first hydraulic unit operating as a pump.

17. Hydraulic apparatus as claimed in claim 16 wherein said valve means include a first valve having a first position hydraulically connecting in said first control position the output of said first hydraulic unit with a consumer, a second position connecting in said second control position the outlets of both said first and second hydraulic units with the consumer, and a third position connecting in said third control position the outlet of said first hydraulic unit with the input of said second hydraulic unit, and a second valve having a first position connecting in said third control position the output of said auxiliary pump with the output ofsaid second hydraulic unit and with the input of said first hydraulic unit, and a second position connecting in said first and second control positions the inlet of said first hydraulic unit and the outlet of said auxiliary pump with said container,

18. Hydraulic apparatus as claimed in claim 15 wherein said operating means are power operated and also connected with said valve means for moving the same between said first, second and third control positions.

19. Hydraulic apparatus as claimed in claim 1 wherein said first and second rotary means include first and second rotary shafts, respectively, having parallel axes; and wherein said connecting means include a transmission mechanically connecting in said engaged condition said first and second shafts for rotation; and comprising a casing enveloping said first and second hydraulic units, said transmission, and portions of said first and second shafts, at least said first shaft having an end portion projecting out of said casing.

won 

1. Hydraulic apparatus with interconnected hydraulic units, comprising, in combination, at least first and second hydraulic units having first and second stator means and first and second rotary means, respectively; connecting means having an engaged position mechanically connecting said first and second rotary means for rotation so that said first and second hydraulic units simultaneously operate as pumps when said first rotary means is driven, and as hydraulic motors when a fluid medium under pressure is supplied to said first hydraulic unit, and a disengaged condition disconnecting said first and second rotary means so that only said first unit operates as pump or motor, respectively; and operating means for placing said connecting means selectively in said engaged and disengaged conditions.
 2. Hydraulic apparatus as claimed in claim 1 comprising casing means enveloping said hydraulic units.
 3. Hydraulic apparatus as claimed in claim 2 wherein said casing means include first and second high-pressure ports and first and second low-pressure ports for said first and second hydraulic units, respectively; high-pressure conduit means and low-pressure conduit means communicating with said first and second high-pressure ports, and with said first and second low-pressure ports, respectively; and check valve means separating said second high-pressure port from said first high-pressure port and said high-pressure conduit means.
 4. Hydraulic apparatus as claimed in claim 1 wherein said first rotary means includes a shaft; and wherein said second hydraulic unit includes a stationary shaft secured to said second stator means and supporting said second rotary means for rotation.
 5. Hydraulic apparatus as claimed in claim 1 wherein said connecting means include a first gear fixedly secured to one of said first and second rotary means for rotation therewith, and a second gear mounted on the other of said first and second rotary gears for rotation therewith about parallel axes in an engaged position meshing with said first gear, and for axial movement to a disengaged position; and wherein said operating means is connected with said second gear for moving the same between said engaged and disengaged positions.
 6. Hydraulic apparatus as claimed in claim 1 wherein said connecting means include first and second gears fixedly secured to said first and second rotary means for rotation therewith about parallel axes, and a third gear operable by said operating means between a position meshing with said first and second gears for connecting the same for rotation in said engaged condition of said connecting means, and a disengaged position spaced from at least one of said first and second gears.
 7. Hydraulic apparatus as claimed in claim 1 wherein said first and second rotary means include first and second slanted wobble plates connected by said connecting means in said engaged position for rotation; and wherein said first and second stator means include first and second cylinder blocks, and first and second pistons in the same, respectively.
 8. Hydraulic apparatus as claimed in claim 1 wherein said first and second stator means are first and second slanted swashplates; and wherein said first and second rotary means include first and second cylinder blocks and pistons in said cylinder blocks sliding on said swasHplates; and wherein said connecting means connect in said engaged condition said cylinder blocks for rotation.
 9. Hydraulic apparatus as claimed in claim 8 wherein said first and second cylinder blocks have parallel axes of rotation; wherein said first and second swashplates are mounted for tilting movement about two parallel axes respectively intersecting with said axes of rotation; and comprising a control means common to both said hydraulic units and operable for simultaneously tilting said first and second swashplates for simultaneously adjusting the output of said first and second hydraulic units.
 10. Hydraulic apparatus as claimed in claim 1 wherein said first rotary means includes a first shaft adapted to be driven by a prime mover when said first hydraulic unit operates as a pump; wherein said second rotary means includes a second shaft adapted to serve as an output shaft when said second hydraulic unit is operated as a hydraulic motor; and comprising valve means having a control position for hydraulically connecting said first and second hydraulic units when said connecting means is in said disengaged condition so that said first hydraulic unit operating as a pump drives said second hydraulic unit operating as a hydraulic motor whereby said first and second hydraulic units form a hydrostatic transmission.
 11. Hydraulic apparatus as claimed in claim 10 comprising an output shaft; and coupling means having a disengaged position and a coupling position for connecting said second shaft with said output shaft when said first shaft is driven by a prime mover and said first and second hydraulic units operate as a hydrostatic transmission.
 12. Hydraulic apparatus as claimed in claim 11 wherein said operating means include shifting means connected with said coupling means and operating the same simultaneously with said connecting means so that said connecting means is in said disengaged condition when said coupling means is in said coupling position.
 13. Hydraulic unit as claimed in claim 12 wherein said connecting means includes a gear transmission connecting said first and second rotary means for rotation in said engaged condition, and including a gear movable to an inoperative position for disconnecting said first and second rotary means in said disengaged condition; wherein said second shaft is axially aligned with said output shaft; and wherein said coupling means includes a coupling sleeve mounted on said second shaft, and for axial movement into engagement with said output shaft; and wherein said shifting means is connected with said gear and said coupling sleeve for simultaneously displacing the same.
 14. Hydraulic apparatus as claimed in claim 10 comprising an auxiliary pump; and wherein said valve means in said control position hydraulically connects the output of said auxiliary pump with the input of said first hydraulic unit operating as a pump, said valve means having another position disconnecting said auxiliary pump from said first hydraulic unit.
 15. Hydraulic apparatus as claimed in claim 1 wherein said first rotary means includes a first shaft adapted to be driven by a prime mover so that said first rotary unit operates as a pump; wherein said second rotary means includes a second shaft adapted to serve as an output shaft when said second hydraulic unit operates as a hydraulic motor; comprising valve means and conduit means hydraulically connecting said first and second hydraulic units, said valve means being operable between a first control position in which in said disengaged condition of said connecting means said first hydraulic unit operates as a pump, a second control position in which in said engaged condition said first and second hydraulic units both operate as pumps, and a third control position hydraulically connecting said first and second units so that in said disengaged condition of said connecting means, said second hydraulic unit operates as a hydraulic motor hydraulically driven by said first unit operating as a pump and forming a hydrostatic transmission with the same.
 16. Hydraulic apparatus as claimed in claim 15 comprising an auxiliary pump and a container for a fluid medium communicating with the low-pressure inlet of said auxiliary pump; and wherein in said third control position said valve means hydraulically connect the high-pressure outlet of said auxiliary pump with the input of said first hydraulic unit operating as a pump.
 17. Hydraulic apparatus as claimed in claim 16 wherein said valve means include a first valve having a first position hydraulically connecting in said first control position the output of said first hydraulic unit with a consumer, a second position connecting in said second control position the outlets of both said first and second hydraulic units with the consumer, and a third position connecting in said third control position the outlet of said first hydraulic unit with the input of said second hydraulic unit, and a second valve having a first position connecting in said third control position the output of said auxiliary pump with the output of said second hydraulic unit and with the input of said first hydraulic unit, and a second position connecting in said first and second control positions the inlet of said first hydraulic unit and the outlet of said auxiliary pump with said container.
 18. Hydraulic apparatus as claimed in claim 15 wherein said operating means are power operated and also connected with said valve means for moving the same between said first, second and third control positions.
 19. Hydraulic apparatus as claimed in claim 1 wherein said first and second rotary means include first and second rotary shafts, respectively, having parallel axes; and wherein said connecting means include a transmission mechanically connecting in said engaged condition said first and second shafts for rotation; and comprising a casing enveloping said first and second hydraulic units, said transmission, and portions of said first and second shafts, at least said first shaft having an end portion projecting out of said casing. 